Ka band propagation experiments on the Australian low earth orbit microsatellite 'FedSat'
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The emergence of the 20/30 GHz Ka band in satellite communications in recent decades has seen systems designers faced with the problem of severe signal attenuation though atmospheric effects, especially rain. Previous experimental missions, such as ACTS and OLYMPUS, have succeeded in collecting large amounts of propagation data, which has led to the development of various semi-empirical models for link design. However, all these experiments were carried out over geostationary satellites, and with a recent tendency towards constellations of low-earth orbit satellites for true global coverage and increased system capacity for real-time services, these models are in need of adaptation for variable elevation angles and the effects of rapid satellite movement. The work contained in this largely experimental thesis presents the Australian ‘FedSat’ LEO microsatellite, carrying a Ka band beacon and a bent-pipe mode transponder, as an ideal research platform for such investigations. The inhouse design, deployment and operation of a very low-cost, fast-tracking earth station is examined in-depth, and particular attention is paid to systems design aspects involving numerous hardware and software technologies, which interact with each other in a highly complex manner, for example Doppler frequency tracking, pointing accuracy control and precise signal power measurements. Prior to and during the operational phase, several crucial design improvements are discussed, implemented and verified. Successful and reliable tracking by using pointing coordinates derived from two-line elements, as opposed to GPS data, is experimentally proven. The design of the earth station prototype is validated by the collection of Ka band propagation data in both beacon and bent pipe modes. After postprocessing of the data, attenuation results for various weather conditions and down to elevation angles well below 10 degrees are illustrated and interpreted in conjunction with the prevailing weather conditions. While a comparison with the measurements from geostationary satellites widely confirms the validity of the results, other interesting phenomena are unveiled that require further investigation. In particular, the extent of low-angle scintillation appears to be wider band than previously reported in published literature, which is a potentially important finding. Finally, the experience gathered during the late-stage design and the operation of the earth station gives rise to several recommendations for further design improvements and operational strategies, which may be helpful for future research groups in this field wishing to conduct similar LEO Ka band propagation experiments on a low budget.
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